if i'm romney, you try to create that momentum. he saw a sign to do it. >> of the eight presidential races in the past 10 where the leads were cut or flipped by the opponent, the average of the comebacks was roughly 5%. in some cases it was a debate that moved the needle. harris? >> mike, thank you of the let's go to syria where the u.n. is estimating more than 20,000 citizens have died in the uprising against the government in the past year and a half. [gunfire] >> obviously you can hear the gunfire as fighting between the rebels and government forces in aleppo intensifies. one activist saying no one is making gains. this has been a key point for them fighting there, and people there are so frightened of the snipers they're leaving dead bodies lying in the streets. >>> meanwhile the fighting sparking a major fire in the city's medieval market. this was actually once a major tourist attraction and world heritage site. activists say there was shelling and gunfire, and some 100 shops were destroyed. >>> now to yemen, they're saying o